This application claims priority under 35 USC § 119 to Korean Patent Application No. 2004-44515, filed on Jun. 16, 2004, the contents of which are herein incorporated by reference in their entirety for all purposes.
1. Field of the Invention
The present invention relates generally to wireless receivers, and in particular to a quadrature voltage controlled oscillator used within a wireless receiver for generating oscillation signals with automated phase control.
2. Description of the Related Art
FIG. 1 shows a conventional wireless receiver as disclosed in U.S. Pat. No. 6,462,626 entitled “Quadrature Output Oscillator Device”. Referring to FIG. 1, the conventional receiver includes an antenna 12 for receiving an RF (radio frequency) signal. The RF signal is filtered by a filter 14 and amplified by an amplifier 16.
The filtered and amplified RF signal is then applied to a first mixer 18 and a second mixer 20 of a first mixing stage 21. The first mixer 18 uses an in-phase oscillation signal Ia generated by a first quadrature voltage controlled oscillator 22. The second mixer 20 uses a quadrature-phase oscillation signal Qa generated by the first quadrature voltage controlled oscillator 22.
An output of the first mixer 18 is provided to a third mixer 24 and a fourth mixer 26 of a second mixing stage 27. The third mixer 24 uses an in-phase oscillation signal Ib generated by a second quadrature voltage controlled oscillator 29, and the fourth mixer 26 uses a quadrature-phase oscillation signal Qb generated by the second quadrature voltage controlled oscillator 29.
The second mixer 20 generates an output provided to a fifth mixer 28 and a sixth mixer 30. The fifth mixer 28 uses the in-phase oscillation signal Ib, and the sixth mixer 30 uses the quadrature-phase oscillation signal Qb. Outputs of the third and sixth mixers 24 and 30 are provided to a selector 32 that generates an in-phase representation IFI of the RF signal. Outputs of the fourth and fifth mixers 26 and 28 are provided to a selector 34 that generates a quadrature-phase representation IFQ of the RF signal. Depending on the phases of the oscillation signals applied to the various mixers, a desired down-converted signal is obtained with the selector 32 acting as an adder and the selector 34 acting as a subtractor, or vice versa, with the selector 32 acting as a subtractor and the selector 34 acting as an adder.
The second quadrature voltage controlled oscillator 29 generates oscillation signals at a much lower frequency, compared to the first quadrature voltage controlled oscillator 22. For example, the frequency of the RF signal received at the antenna 12 is around 1.9 GHz. The frequency of the oscillation signals generated by the first quadrature voltage controlled oscillator 22 is in a range from about 1.5 to about 1.7 GHz. The second quadrature voltage controlled oscillator 29 generates oscillation signals with a difference frequency between the frequency of the RF signal received at the antenna 12 and the frequency of oscillation signals generated by the first quadrature voltage controlled oscillator 22. For example, the difference frequency is in a range from about 200 MHz to about 400 MHz.
The mixers within the receiver of FIG. 1 are used to down-convert the frequency of the RF signal received at the antenna 12 to an intermediate frequency. An image signal has a frequency lower than the oscillation frequency. The image signal is down-converted to the same intermediate frequency as the received radio signal. The down-converted image signal may interfere with the desired down-converted radio signal and degrade the receiver's performance.
To reject the image signal, extra image-rejection filters may be used before the mixers. However, integration of such extra filters on to the same circuit as the receiver in FIG. 1 is difficult. Therefore, the mixers within the receiver are used here to eliminate the down-converted image signal. The quality of the mixers is determined by a quadrature phase relationship between oscillation signals generated by the first quadrature voltage controlled oscillator 22. For example, the down-converted image signal may not be completely eliminated without a precise quadrature relationship between the in-phase component I and the quadrature phase component Q generated by the first quadrature voltage controlled oscillator 22.
FIG. 2 shows a block diagram of a quadrature voltage controlled oscillator as disclosed in U.S. Pat. No. 6,456,167 entitled “Quadrature Oscillator”. Referring to FIG. 2, the conventional quadrature voltage controlled oscillator includes a first oscillation circuit 100, a second oscillation circuit 200, and current sources I1 and I2. In-phase components IP and IN output from the first oscillation circuit 100 are applied to input terminals of the second oscillation circuit 200. Quadrature components QP and QN output from the second oscillation circuit 200 are applied to input terminals of the first oscillation circuit 100, respectively. The in-phase components IP and IN and quadrature components QP and QN are applied to mixers 18 and 20 in the receiver of FIG. 1 for example.
However, the in-phase components of the voltage controlled oscillator may not have an ideal quadrature relationship with the quadrature-phase components. That is, a phase difference between the in-phase components and the quadrature-phase components may be 90°+ERR, with ERR being an error component. Such an error in the phase difference is mainly due to device mismatch in the voltage controlled oscillator. With such an error, a passive filter may be used to reject the resulting image signal from the received radio frequency in a receiver. However, such a passive filter within the receiver complicates the design and increases the chip size of the receiver.
Therefore, the quadrature voltage controlled oscillator needs to be precisely controlled so that the in-phase signal and the quadrature-phase signal have the proper quadrature relationship for desired receiver performance. U.S. Pat. No. 6,462,626 discloses a quadrature oscillator device that controls a gain of an amplifier.
In U.S. Pat. No. 6,462,626, an amplifying ratio of the amplifier in the quadrature oscillator device is controlled for a precise quadrature relationship between an in-phase signal component I and a quadrature phase signal component Q. However, such a gain adjustment may be manual after measurement of the in-phase and quadrature signal components I and Q. Such manual adjustment may be time-consuming and prone to error. Thus, an efficient and accurate mechanism for automatically controlling the quadrature relationship between the in-phase and quadrature signal components I and Q is desired.